Microwave power divider



J. Fl ZALESKI Oct. 9, 1956 MICROWAVE POWER DIVIDER Filed April 2, 1955United States Patent Ofiice 2,766,430 iatented Oct. 9, 1956 2,766,430MICROWAVE POWER DIVIDER John F. Zaleski, Thornwood, N Y., assignor toGeneral Precision Laboratory Incorporated, a corporation of New YorkApplication April 2, 1953, Serial No. 346,330

6 Claims, (Cl. 333-7) This invention relates to adjustable microwavepower dividers and attenuators, which are wide band, have constantimpedance and high breakdown potential.

The problem of attenuating large amounts of microwave pulsed powerpresents problems not met in controlling electricity at lowerfrequencies. It has not been found simple to attenuate large powerswithout encountering spark-over and serious changes of the impedancepresented to the source of power.

One of the methods of microwave attenuation involves the use of anadjustable power divider and this method is employed in the instantinvention to provide a device having constant input impedance, wide bandoperation, and a high spark-over potential.

The instant invention is based upon the properties of that form of themicrowave hybrid junction known as the magic tee. It also depends uponthe properties of a round hollow microwave guide. This type of guide iscombined with rectangular hollow guide to form a magic tee having twocollinear arms made of round guide and series and shunt arms ofrectangular guide, the assembly constituted by these four arms beingrotatable relative to the fixed input and output waveguides. Themicrowave power is introduced to the round guide, setting up a TE1,1non-symmetrical field therein. The rectangular guide arms comprise aseries or E arm and a shunt or H arm and are rotatably positioned sothat they may either intercept all of the energy permitting none topass, or may intercept none and permit all to pass, or may beintermediately positioned to intercept some, permitting the remainder topass.

If the series arm and shunt arm are terminated in nonreflectingdissipative elements all energy taken out of the round guide by them isdissipated in heat, and whatever energy is not removed by the series andshunt arms may be utilized at an exit further along in the round guide.The amount of energy available at this exit is thus easily controlled byrotation of the rotatable guide section comprising the hybrid juction.With proper termination and impedance matching of the several arms, nochange of impedance is reflected to the source as the attenuator isadjusted. The device is only slightly frequency sensitive, and the powercarrying capacity is nearly as high as that of a straight length ofhollow guide of the same size.

One purpose of this invention is to provide a simple microwave dividerfor dividing a quantity of microwave energy into three parts, the ratioof one part to the other two being adjustable in any proportion, andthese two parts being equal.

Another purpose of this invention is to provide a simple and improvedmicrowave power attenuator.

A furtherunderstanding qf this invention may be secured from thedetailed description and the associated drawings, in which:

Figure 1 is an isometric representation of an embodiment of theinvention.

Figures 2 and 3 illustrate field modes which may be set up in the guidejunction of Figure 1.

Referring now to Fig. 1, a round conductive hollow pipe 11 suitable fortransmission of microwave energy is so excited as to transmit microwaveenergy in the TE1,1 mode. Any microwave frequency at which round andrectangular hollow guides can be used may be employed as, for examplethe x-band frequency of 10,000 megacycles, and in this example the roundguide 11 has a suitable diameter for this frequency. It may beconveniently excited by microwave energy introduced by a rectangularguide 12 connected to round guide 11 through a guide transformer or, asshown, through an end plate 13 with a suitable coupling iris such as theinductive iris 14 in the end of the rectangular guide. Any equivalentmeans of matching the rectangular guide impedance to that of the roundguide may of course be employed. When the rectangular guide carriesmicrowave energy in the TE1,0 mode, the TE1,1 mode is excited in theround guide, and microwave energy is transmitted through the round guidein that mode.

The other end of the round guide is arranged in any convenient way forthe utilization of energy passing through it. For example, as there areseveral advantages in the use of rectangular guide for microwavetransmission, a transition torectangular guide may be made by anyconvenient means as, for example by the same means used at the inputend. A flat end plate 16 is used to terminate the round guide andcarries a rectangular hollow guide 17 with the direction of its shortercross sectional dimension parallel to the direction of the shorter crosssectional dimension of input guide 12. The guide 17 is appropriatelyimpedance matched by any means, for example'by an iris 18. In addition,the guide 17 is terminated in its own characteristic impedance toprevent refiection of energy.

1 At an intermediate cross sectional plane of the round guide 11 twoside arms 19 and 21 made of rectangular hollow guide are attached atright angles to the round guide. One arm 19 has its longer crosssectional dimension in the plane of the round guide cross section andtherefore constitutes a series or. E side arm. The other arm 21 has itslonger cross sectional dimension parallel to the axis of the round guideand therefore constitutes a shunt or H side arm. The two side arms arespaced circumferentially apart on the round guide. These series andshunt side arms together with the round guide thus form a magic tee withthe collinear arms consisting of round guide sections and the series andshunt arms of rectangular guide sections. This magic tee behaves I ike amagic tee made entirely of rectangular guide provided that the fieldmode in the round guide is TE1,1 and further provided that this mode isso oriented as to excite the maximum amount of energy in the TE1,1) modein the rectangular side arms. The usual provisions as to internalmatching should be observed to avoid reflections. This may be done bythe use of buttons, rods, septums or irises at the junction, one simpleway being to insert irises in the side arms as indicated at 22 and 23.

The portion 11A of the round guide 11 containing through rectangularguide 12- excites the TE1,1 mode in round guide 11. This field mode isas depicted in the proper direction to excite the TE1,0 mode in bothside arms 19 and 21, and all of the energy divides into two equal partsand passes out of these arms, the field relationships being indicated inFig. 2. Since the series arm 19 extends in the direction of the E-vectorof the field, represented by the lines in the round guide, it hasmaximum voltage coupling to the interior of the round guide and isexcited to the maximum. Also the shunt arm 21, extending perpendicularlyin the E-vector direction, has maximum current coupling and excitation.Since all of the energy is taken by the side arms, no energy passes themand there is no output from the end guide 17.

When the round guide section 11A is rotated in either direction by 90,as indicated in Fig. 3, the attitudes of both side arms become suchrelative to the TE1,1 field in the round guide 11A as to prevent anyenergy entering either side arm. The microwave energy accordingly passesthrough the round guide unhindered and all of it leaves the round guidethrough the end rectangular guide 17.

At intermediate positions of the rotatable section 11A, lesser amountsof energy are abstracted by the side arms 19 and 21, the remainder ineach case passing out guide 17. In each case the amount of energyabstracted by the side arms is equally divided between them.

A useful application of this invention in which no flexible armconnections are required is in the control of microwave power byattenuation without change of impedance reflected to the source. In thisapplication the arms 19 and 21 are terminated in resistivepowerabsorbing loads. These may be of the wedge type as indicated at 27and 28, and may be made compact and integral with the side arms. Thewedges 27 and 28 may be made of finely divided iron in an insulatingsolid matrix, commonly known as polyiron. In the position shown withinput at 12, all energy passes into the side arms and is absorbed, whilenone reaches the output arm 17. In the position at 90 to that shown allenergy reaches 17 and none is absorbed, while in intermediate positionsintermediate amounts of energy reach the output guide 17.

In place of employing the guide 17 as the single outlet arm of theattenuator this arm may be terminated in a resistive non-reflective loadand two useful loads may be placed to terminate the arms 19 and 21,instead of the dissipative loads 27 and 28.

What is claimed is:

1. A device of the class described comprising, a round hollow microwaveguide suitable for transmission of microwave energy at a selectedfrequency in the TE1,1 mode having a specific voltage vector direction,a portion of said round hollow microwave guide constituting the twocollinear arms of a magic tee hybrid junction extending in eitherdirection from a selected point in the common axis thereof, and tworectangular guide side arms extending mutually at right angles from saidround hollow microwave guide orthogonally at said selected point, onesaid side arm being a series arm and the other said side arm being ashunt arm, and means for adjustably efiecting rotation of the two saidside arms in concert relative to said specific voltage vector direction.

2. A device of the class described comprising, a round hollow microwaveguide suitable for transmission of microwave energy at a selectedfrequency in the TE1,1 mode, means for exciting the TE1,1 mode of fieldtransmission of microwave energy having a selected voltage vectordirection in said round hollow microwave guide, a portion of said roundhollow microwave guide constituting on either side of a selected pointin the axis thereof the two collinear arms of a magic tee hybridjunction, two rectangular guides constituting the two side arms of saidmagic tee hybrid junction extending mutually at right angles from saidround hollow microwave guide orthogonally at said selected point in theaxis, one said side arm being a series arm and the other said side armbeing a shunt arm, and means for adjustably rotating said side arms inconcert about said axis to any angular position within relative to saidselected voltage vector direction, whereby the amount of energyabstracted equally by said side arms from said round guide is variedbetween zero and the full amount of the input energy.

3. A device of the class described comprising, a round hollow microwaveguide suitable for transmission of microwave energy at a selectedfrequency in the TE1,1 mode, a portion of said round hollow guideconstituting on either side of a selected point in its axis the firstand second collinear arms of a magic tee hybrid junction, a rectangularhollow input guide suitable for transmitting microwave energy at saidselected frequency in the TEm mode, means for coupling said rectangularhollow input guide coaxially to one end of the first collinear arm ofsaid round hollow microwave guide, two rectangular hollow guidessuitable for transmitting microwave energy at said selected frequency inthe TE1,0 mode, said two guides being joined to said round guide at saidselected point, said two rectangular guides being perpendicular to saidaxis and perpendicular to each other and constituting two magic tee sidearms, one said side arm being oriented at the juncture as a series armand the other said side arm as a shunt arm, and means for adjustablyrotating said side arms in concert about said axis and the longitudinalaxis of said rectangular input guide to any angular position of saidseries arm within 90' of the direction of the lesser cross sectionaldimension of said rectangular hollow input guide.

4. A device of the class described in accordance with claim 3 includingmeans for deriving microwave energy from said second collinear arm.

5. A microwave power divider comprising, a round hollow microwave guidesuitable for transmission of microwave energy at a selected frequency inthe TEl,1 mode, said round guide constituting on either side of aselected point in its axis the first and second collinear arms of amagic tee, a rectangular hollow input guide suitable for transmittingmicrowave energy at said selected frequency in the TE1,0 mode, means forcoupling said input guide coaxially to the distal end of said firstcollinear arm, a rectangular hollow output guide suitable fortransmitting microwave energy at said selected frequency in the TE1,0mode, means for coupling said output guide coaxially to the distal endof said second collinear arm, with the shorter cross sectional dimensionthereof parallel to the shorter cross sectional dimension of said inputguide, two rectangular hollow guide side arms suitable for transmittingmicrowave energy at said selected frequency in the TEi,o mode, said sidearms being joined to said round guide at said selected point in its axisand perpendicular thereto and to each other, one said side arm beingoriented as a series arm and the other said side arm being oriented as ashunt arm, and a pair of rotatable joints in the round guide on eitherside of said selected point in the axis whereby the two side arms andassociated round guide section may be rotated around said axis between aposition in which the series arm is parallel to the direction of theshorter cross-sectional dimension of said input guide to a position inwhich the shunt arm is parallel to said dimension.

6. A device of the class described in accordance with claim 5 in whicheach of said rectangular side arms is terminated in a resistivenon-reflective load.

References Cited in the file of this patent UNITED STATES PATENTS2,526,383 Meier Oct. 17, 1950 2,584,399 Preston Feb. 5, 1952 2,603,710Bowen July 15, 1952 2,606,248 Dicke Aug. 5, 1952 2,634,331 Honda Apr. 7,1933 FOREIGN PATENTS 635,760 Great Britain Apr. 19, 1950

